JP2003105594A - Closed system electrodeposition coating system and electrodeposition coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodeposition coating system and electrodeposition coating method which make the effective utilization of coating material components possible and achieve a high degree of a closed system by suppressing the overload of a filter equipment relating to washing water in an advanced washing process step and recycling the coating material components. SOLUTION: The electrodeposition coating system of a closed system which has an electrodeposition tank 1 for electrodeposition coating of a material to be coated, first ultrafiltration means 8 for performing ultrafiltration of an electrodeposition coating material 15, recovering and washing tanks 2 to 4 for washing the material to be coated, advanced washing tanks 5 and 6 for performing advanced washing of the material to be coated, a concentration tank 7 for accepting the overflow water thereof, concentrated water feeding means 13 for feeding the concentrated water 21 thereof to the electrodeposition tank 1, a filtrate tank 23 for storing the filtrate of the first ultrafiltration means 8 and reverse osmosis membrane filtration means 10 for extracting the liquid of the filtrate tank 23 and filtering the same by a reverse osmosis membrane and comprises sending the concentrate to the recovering and washing tank 4 and sending the filtrate to the advanced washing tanks 5 and 6 or removing the same to the outside of the system and the electrodeposition coating method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed system electrodeposition coating apparatus and an electrodeposition coating method that reduce the loss of electrodeposition coating material and at the same time discharge little or no coating components from the electrodeposition coating facility.

[0002]

2. Description of the Related Art Electrodeposition coating is widely applied by taking advantage of its manageability, economy, etc., and the technological progress is remarkable. Particularly in the automobile field, it has been more than 15 years since the conversion from anion electrodeposition coating to cation electrodeposition coating was attempted, and today almost 100% is cation electrodeposition coating. Cationic electrodeposition coating has been introduced not only in the field of automobiles but also in a wide range of fields such as building materials, general metal products, electrical products, and industrial machines.

The background behind the development of cationic electrodeposition coating suitable for coating automobiles is U.
Development of cationic electrodeposition coating with excellent F (ultrafiltration) characteristics,
There was development of a UF film suitable for cationic electrodeposition coating and development of a UF system that makes full use of these.

In the thus developed cationic electrodeposition coating system, a cleaning step is provided after electrodeposition of an object to be coated. That is, the undried coating film electrodeposited in the electrodeposition tank is baked and dried in a drying furnace,
Although the coating of the object to be coated is completed, on the undried coating film pulled up from the electrodeposition tank, paint in the tank (paint component of non-electrodeposition),
Negatively charged counter ions, etc. are attached. If this is left as it is and baked and dried, defective finishes called sagging, peeling, stripes, and lumps occur. In order to avoid this, in a general electrodeposition coating system, after the electrodeposition, a washing step is performed, and then drying-baking is performed.

In the washing step after electrodeposition, generally, an electrodeposition tank liquid or a cleaning waste liquid containing a relatively large amount of paint is filtered, a recovered liquid containing paint components is washed into the electrodeposition tank, and a filtrate is washed. It is divided into two processes, a closed circuit washing process (recovery washing process) in which the water is returned as water and circulated and reused, and a final washing process (advanced washing process) provided as a separate process as a subsequent process. The former can collect and wash the paint components adhering to the coating object by washing the coating object with a filtrate obtained by subjecting the coating material in the electrodeposition tank to UF treatment. The latter is a very important step for performing high-level cleaning, and pure water,
Finishing water is washed with water such as industrial water and tap water to wash diluted paint components and counter ions that cannot be removed in the recovery water washing process, and the washing waste liquid is discharged outside the system. Is the current situation.

However, the amount of water required for this final washing is generally very large, and since the washing waste liquid contains a small amount of paint and miscellaneous ions, it cannot be discharged to the outside. It is not allowed, and special treatment technology for the final washing waste liquid is required from the environmental and economic perspectives.

A technique of reusing the waste liquid of the final washing step without discarding it is disclosed in International Publication WO96 / 07775. The technology is to separate the filtrate and the concentrated liquid containing the paint components by circulating the waste liquid discharged from the final washing tank to a filtration device equipped with a semipermeable membrane while maintaining a predetermined pH in the concentration tank. It is characterized by doing. However, in this case, although the separated filtrate can be used as the final washing water, the concentrated solution is basically discarded, and disposal of the concentrated solution containing the paint at a high concentration poses a problem.

It is conceivable to return this concentrated liquid to the electrodeposition tank, but a line that often brings washing water from the pretreatment process to the electrodeposition tank, a line that supplies a small amount of pure water, seasonal factors and equipment-related factors. In a line where evaporation of the liquid from the electrodeposition tank is small due to various factors, the concentrated liquid is returned to cause the liquid level in the electrodeposition tank to rise, and it is possible to return all of the concentrated liquid to the electrodeposition tank. , Often difficult. At this time, it is possible to lower the total amount of the concentrated liquid by increasing the concentration of the concentrated liquid to balance the amount of the electrodeposition liquid in the electrodeposition tank. When trying to improve the capacity of the semipermeable membrane, the load of the module of the semipermeable membrane becomes too large, and the life of such a module becomes extremely short, which is disadvantageous in terms of man-hours and cost. Become.

[0009]

Therefore, the present invention is
Regarding the final washing water in the final washing process (advanced washing process), it is possible to reduce or eliminate the paint components to be discarded by reusing the paint components without overloading the filtration device. An object of the present invention is to provide a closed system electrodeposition coating apparatus and an electrodeposition coating method capable of achieving a high degree of closure of the entire electrodeposition coating apparatus.

[0010]

As a result of intensive studies in view of the above problems, the present inventor has found that the following problems can be solved by the present invention, and has arrived at the present invention.

That is, the closed-system electrodeposition coating apparatus of the present invention includes at least an electrodeposition tank for containing the electrodeposition paint, dipping an object to be coated and electrodeposition coating, and an electrodeposition paint extracted from the electrodeposition tank. Is ultrafiltered and the concentrated liquid is returned to the electrodeposition tank, and the collected washing water containing the filtrate from the ultrafiltration means is housed, and the electrodeposition is performed in the electrodeposition tank. Replenishing the painted objects by washing each tank with one or more tanks for collecting water, which is a pre-stage feed of the collected washing water to the electrodeposition tank. Washing water containing pure water is accommodated, and one or two or more washing tanks for highly-washing each of the objects to be washed washed in the one or two or more recovery washing tanks, and Two
In the case of more than the tank, the advanced washing tank in which the washing water is fed in the first stage, the concentration tank that receives the overflow water of the frontmost tank of the advanced washing tank, and the ultrafiltration of the water extracted from the concentration tank Then, the filtrate is sent to any of the advanced water washing tanks and / or removed outside the system, and the concentrated liquid is returned to the concentrated tank, whereby the water received in the concentrated tank is used as concentrated water. An electrodeposition coating apparatus comprising a second ultrafiltration means and a concentrated water delivery means for delivering the concentrated water to the electrodeposition tank, further comprising the first ultrafiltration means. A filtrate tank for storing the filtrate of the above, a recovered water washing water sending means for sending the liquid in the filtrate tank to the last stage of the recovered water washing tanks, and a liquid extracted from the filtrate tank is filtered by a reverse osmosis membrane. Reverse osmosis membrane filtration means for Back to the tank, the filtrate of the reverse osmosis membrane filtration unit, the sending highly water washing tank to either, and / or, and removing out of the system.

Here, the "pre-stage feed" means that the liquid such as washing water is replenished into the tank from the outside and at the same time, the surplus liquid is sent to the tank in the previous step, thereby balancing the tank liquid volume. Means to maintain the purity of. As a means for sending the liquid to the tank of the previous step, a so-called overflow method is generally used, in which the liquid surface of the post step is kept higher than that of the previous step, and the liquid is overflowed from the tank and dropped into the previous step. The tanks of the process (1) may be simply connected by a communication pipe, or may be used as a means for sending a liquid by a pump. In the present invention, these means are also included in the concept of "overflow".

On the other hand, the closed system electrodeposition coating method of the present invention includes at least an electrodeposition coating step of immersing an object to be coated in an electrodeposition tank containing an electrodeposition coating material, and one or two or more recovery washing tanks. The collected washing water contained in the above-mentioned electrodeposition tank was used to sequentially wash the objects to be electrodeposited in each of the collecting water washing tanks, and the collecting water washing step was carried out in one or more advanced washing tanks. , With wash water containing makeup pure water,
An advanced electrodeposition coating method comprising: an advanced water washing step of performing advanced water washing for each of the advanced water washing tanks on the object washed in the recovered water washing step, wherein the recovered water wash water of each recovered water wash tank in the recovered water wash step is In the advanced water washing step, the pre-stage feed is finally sent to the electrodeposition tank, and when the advanced water washing step has two or more advanced water washing tanks, the advanced washing water in each advanced water washing tank is used as the first step feed in the advanced water washing step. The overflow water of the first-stage tank of the advanced washing tank is received in the concentrating tank, the water extracted from the concentrating tank is ultrafiltered, and the filtrate is sent to any of the advanced washing tanks, and / or By removing it to the outside of the system and returning the concentrated solution to the concentrating tank, the water received in the concentrating tank becomes concentrated water, and a part or all of the concentrated water is sent to the electrodeposition tank, Electrodeposition coating from the electrodeposition tank in the electrodeposition coating process The withdrawal, which was ultrafiltration,
The concentrated liquid is returned to the electrodeposition tank, the filtrate is stored in a filtrate tank, the liquid extracted from the filtrate tank is filtered by a reverse osmosis membrane, and the concentrated liquid by the reverse osmosis membrane is returned to the filtrate tank. It is characterized in that the liquid in the filtrate tank is sent to the last tank of the recovered water washing tanks, while the filtrate is sent to any of the advanced water washing tanks and / or removed outside the system.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The closed system electrodeposition coating apparatus and electrodeposition coating method of the present invention will be described in detail below with reference to preferred embodiments. Figure 1
Closed system electrodeposition coating apparatus that is an embodiment of the present invention (hereinafter sometimes simply referred to as "electrodeposition coating apparatus")
It is a schematic block diagram which shows the outline (flow) of FIG. In FIG. 1, the electrodeposition coating apparatus according to the present embodiment basically comprises an electrodeposition tank 1 containing an electrodeposition coating material 15, recovery water wash water 16, 17,
Recovery water washing tanks 2, 3 and 4 respectively containing 18 and advanced water washing tanks 5 and 6 respectively containing washing water 19 and 20 containing supplementary pure water are arranged in series. In addition,
The “series arrangement” here does not mean that the arrangement is physically aligned in a straight line, but means that the respective tanks are arranged so as to be sequentially performed in the process.

The object to be coated by electrodeposition is immersed in the electrodeposition coating material 15 contained in the electrodeposition tank 1 by a transporting device (not shown) and electrodeposition coating is performed [electrodeposition coating step]. In addition, in the present invention, when the term "electrodeposition coating" is used, it means a state in which coating film components are electrically attached to an object to be coated by electrodeposition, and baking and drying are performed to finally form an electrodeposition coating film. Will be distinguished by using the expression “completion of electrodeposition coating”.

Thereafter, the object to be coated pulled up from the electrodeposition coating material 15 is successively washed with the collected water washing tanks 2, 3 and 4 [recovered water washing step], and further successively washed with the advanced water washing tanks 5 and 6 [ Advanced water washing process]. The washing of each of these tanks with water is carried out by a liquid contacting means such as a spray to wash away the non-electrodeposited coating components and counter ions and other contaminants adhering to the surface. Since the impurities such as the above-mentioned paint components are brought into the recovered water washing tanks 2, 3, 4 and the advanced water cleaning tanks 5, 6, the recovered water washing water 16, 17, 18 and the rinse water 19, 2
0 is polluted.

Recovered rinse water 16, 17, 18 in the recovered rinse tanks 2, 3, 4 and rinse water 1 in the advanced rinse tanks 5, 6
Nos. 9 and 20 are respectively fed to the previous stage, and the surface of the object to be coated is cleaned as the process progresses, so that the tank of the previous process has a higher paint concentration and the like.
The object to be coated after the high-level water washing is sent to the baking / drying furnace in the next step and baked / dried to complete the electrodeposition coating.

In FIG. 1, the transfer device, the electrodes and other members in the electrodeposition tank, the baking / drying furnace, etc. are not shown, but these are not particularly limited, and well-known modes and means may be used. Either can be applied. Also, the recovered water washing tanks 2, 3, 4 and the advanced water washing tanks 5, 6 are
Although both are schematically shown in the form of spray water washing, immersion water washing, flow water washing and the like may be appropriately selected or a combination thereof as the liquid contacting means.

The electrodeposition coating material 15 contained in the electrodeposition tank 1 is continuously extracted from the pipe a by the pump 11 and ultrafiltered by the UF filtration device 8 which is the first ultrafiltration means. The concentrated liquid is returned to the electrodeposition tank 1 through the pipe b.
On the other hand, although the filtrate ultrafiltered by the UF filtration device 8 is finally used as the recovered water wash water 18 of the recovered water wash tank 4 on the most advanced water wash tank side (the last stage) of the recovered water wash tanks, It is once stored in the filtrate tank 23. Filtrate tank 23
The liquid inside is supplied to the recovery washing tank 4 through the pipe c by the pump 24. When supplying the liquid to the recovery washing tank 4,
As schematically illustrated, the object to be coated may be sprayed in the recovery water washing tank 4, or may be directly charged into the recovery water washing tank 4.

The collected water washing water 16, 17, 18 in the collected water washing tanks 2, 3, 4 are respectively fed in the preceding stage,
The recovered wash water 18 overflowing the recovered water wash tank 4 is sent to the recovered water wash tank 3, the recovered water wash water 17 overflowed from the recovered water wash tank 3 is sent to the recovered water wash tank 2, and the recovered water wash tank 2 overflowed. The water 16 is finally sent to the electrodeposition tank 1. That is, electrodeposition tank 1, UF
Filtration device 8, filtrate tank 23 and recovered water washing tanks 2, 3,
One closed circuit is formed by 4 (hereinafter referred to as "closed circuit X").

The advanced water washing tank 6 is supplied with pure water from the outside as shown by an arrow D, and contains the supplied pure water. As shown schematically, the makeup pure water may be poured directly onto the article to be coated in the advanced water washing tank 6, or may be directly introduced into the advanced water washing tank 6, but In order to more completely replace contaminants such as ions, it is preferable to pour directly onto the article to be coated. The pure water supplied here is not only water generally called pure water such as deionized water, purified water, and distilled water, but also industrial water, ground water, tap water, and other water, If it is of a purity that can be used as the final step of water washing in electrodeposition coating,
These can also be used as pure water.

The washing water 20 in the advanced washing tank 6 has been fed forward, and the washing water 20 overflowing the advanced washing tank 6 is sent to the advanced washing tank 5. Further, wash water 1 overflowing from the advanced water washing tank 5 which is the first tank
9 is received in the concentrating tank 7, from which a pump 14 is further supplied.
Through the pipe d by the UF which is the second ultrafiltration means.
Ultrafiltration is performed by the filtration device 9. The ultrafiltrated concentrated liquid is returned to the concentration tank 7 through the pipe e. That is,
The concentrating tank 7 and the UF filtration device 9 form a small-unit closed circuit. The liquid in the concentrating tank 7 is circulated and concentrated by this small unit closed circuit, and becomes concentrated water 21.

On the other hand, the filtrate ultrafiltered by the UF filter 9 is temporarily stored in the cushion tank 25. The filtrate stored in the cushion tank 25 is sent to one of the pipes C and D by switching the three-way valve 26. In order to effectively use the filtrate, it is generally sent to the pipe C. However, due to the balance of the liquid amount, even if a part of the filtrate is sent to the pipe D and drained out of the system, the filtrate is still clean, which causes a problem. Absent. The filtrate sent to the pipe C by the switching operation of the three-way valve 26 is passed by the pump 27 through the pipe f to the advanced washing tank 6
Is supplied to. At the time of supplying to the advanced water washing tank 6, the material to be coated may be sprayed in the advanced water cleaning tank 6 as shown schematically, or may be directly charged into the advanced water cleaning tank 6. Further, in the advanced water washing tank 6, when it is desired to perform the advanced water washing only with the pure water supplied from the pipe D, the filtrate ultrafiltered by the UF filtration device 9 is supplied to the advanced water washing tank 5 in the preceding stage. Good.

As described above, the advanced water washing tank 5 to the advanced water washing tank 6
Since it is fed at the first stage during the interval,
6, the concentration tank 7, the UF filtration device 9 and the cushion tank 25 form one closed circuit (hereinafter, referred to as “closed circuit Y”). Since the filtrate from the UF filtration device 9 may be directly sent to the advanced water washing tank 6, the cushion tank 25 is not an essential component in the present invention.
In this way, by cleaning the contaminated washing water 19 in the advanced washing tank 5 and using it in a cycle, the advanced washing tanks 5, 6
It is possible to suppress the outflow of the paint components from the system in the advanced washing step while suppressing the contamination of the washing water 19 and 20 in the above step.

In the electrodeposition coating apparatus of the present embodiment, the liquid flows in and out between the two closed circuits X and Y to balance the amount of the liquid as a whole, and the coating composition as a whole of the device. It is possible to suppress the outflow from the system.

In the closed circuit Y, a part or all of the concentrated water 21 concentrated in the concentrating tank 7 is fed by the pump 13 to the electrodeposition tank 1 through the pipe g (concentrated water feeding means).
As a result, the liquid has moved to the closed circuit X. That is, since the concentrated water 21 is used as the electrodeposition paint 15 without discarding the concentrated water 21 or by reducing the amount to be discarded, it is possible to prevent the paint components from flowing out of the system in the closed circuit Y. At this time, the liquid surface of the electrodeposition tank 1 rises as it is due to the introduction of the concentrated water 21, but in the present embodiment, an amount of liquid corresponding to that amount is extracted from the closed circuit X. .

In the closed circuit X, the filtrate of the UF filtration device 8 is
Once stored in the filtrate tank 23, the liquid in the filtrate tank 23 is extracted by the pump 12 and sent to the RO filtration device 10 having a reverse osmosis membrane as a reverse osmosis membrane filtration means. R
The concentrated liquid filtered by the O filter device 10 is returned to the filtrate tank 23. As described above, the liquid in the filtrate tank 23 joins the pipe c and is sent to the recovery water washing tank 4. On the other hand, R
The filtrate filtered by the O filter device 10 is sent to the three-way valve 22 through the pipe h. By the switching operation of the three-way valve 22, the sent filtrate is sent to one of the pipes A and B. When it is sent to the pipe A, it is drained out of the system as it is. When it is sent to the pipe B, it is supplied to the advanced water washing tank 6 through the pipe i. When supplying to the advanced water washing tank 6,
As schematically shown, it may be directly charged into the advanced water washing tank 6 or may be sprayed on the article to be coated in the advanced water washing tank 6. Further, in the advanced water washing tank 6, when it is desired to perform the advanced water washing only with the pure water supplied from the pipe D, the filtrate filtered by the RO filtration device 10 may be supplied to the advanced water washing tank 5 in the preceding stage. .

As described above, according to the electrodeposition coating apparatus of this embodiment, most of the paint components (solid content) are recovered because the concentrated water 21 concentrated in the concentration tank 7 is almost completely discarded. You can Further, since the filtrate obtained by the RO filtration device 10 does not contain the solvent, acid, amine, etc. in the paint components, even if this is extracted from the closed circuit X including the electrodeposition tank 1, the electrodeposition tank 1 The balance of the paint composition inside will not be lost. Furthermore, since it is not necessary to forcibly increase the concentration of the concentrated water 21 in the concentrating tank 7, no load is applied to the module in the UF filtration device 9, and the module life is not shortened.

The amount of the filtrate from the RO filtration device 10 extracted from the closed circuit X including the electrodeposition tank 1 is the amount when the concentrated water 21 concentrated to the target concentration in the concentration tank 7 is sent to the electrodeposition tank 1. To
The liquid level of the electrodeposition coating material 15 in the electrodeposition tank 1 may be such that it can maintain a normal value. Normally, concentrated water 21 is supplied from the closed circuit Y to the electrodeposition tank 1
When the liquid is not sent to, the pure water is supplied in addition to the paint replenishment in order to maintain the liquid surface of the electrodeposition paint 15. Therefore, the amount of the filtrate from the RO filtration device 10 corresponds to the amount of the concentrated water 21 sent to the electrodeposition tank 1 minus the amount of pure water supplement.

In the present embodiment, a device capable of selecting, with the three-way valve 22, the filtrate filtered by the RO filtration device 10 to be sent to the advanced water washing tank 6 or drained to the outside of the system is exemplified. However, in the present invention, it may be fixed to only one of them, or the advanced water washing tank 6
It is also possible to adopt a configuration in which the liquid is sent to and the drainage to the outside of the system at the same time. Of course, by using a configuration in which the water is sent to the advanced washing tank 5 or 6, efficient use of water resources can be achieved.

Further, in the present embodiment, an example of an apparatus comprising three recovery washing tanks and two advanced washing tanks is given, but each may have only one tank,
It may be two or more tanks. Of course, the final dilution ratio of the washing water to be contained can be increased by increasing the number of both washing tanks, and the high cleaning effect can be obtained. Therefore, it is necessary to appropriately select the optimum number of stages of each washing tank in consideration of the above problems, waste of resources such as water and electric power supplied to the transfer device, and lengthening of the electrodeposition treatment time. Good.

Generally, a semipermeable membrane that can be used for filtration is RO
(Reverse osmosis) membrane, UF (ultrafiltration) membrane, MF (microfiltration)
There are membranes. In this embodiment, the right material is placed in the right place. That is, the UF membrane having a large treatment capacity per unit time and having a sufficient coating material component separating ability is used for the filtering devices 8 and 9 in FIG. On the other hand, the filtration device of reference numeral 10 in FIG. 1 uses an RO membrane, which has a small treatment capacity per unit time, but is further excellent in the ability to remove paint components. The MF membrane is U
It has a pore size larger than F membrane and has excellent membrane treatment capacity, but a large amount of paint components enter the filtrate and the drainage of the filtrate does not meet the water quality standards for drainage, and the filtrate is reused as the final wash water or recovered wash water. In such a case, the cleaning effect is poor, and the coating may be finely solidified on the article to be coated, that is, so-called "spots" may be formed to stain the coating film, which is not preferable.

The UF membrane used in the UF filtration devices 8 and 9 is
Both the throughput and the components in the filtrate have no problem in practical use. The UF membrane has a molecular weight cutoff of 3,000.
Approximately 1,000,000 is preferable, and the material may be any of polyacrylonitrile, polysulfone, polyolefin, and chemically modified products thereof. Since the suitability of the material, the molecular weight cut-off, etc. varies depending on the liquid quality, it is preferable to conduct a preliminary investigation and select it.

The concentrated water 21 in the concentrating tank 7 is preferably kept in a state where the pH is always kept at 6.4 or less by an operation such as addition of an acid, more preferably 6.0 or less, and more preferably 4.
It is more preferable to adjust it between 5 and 6.0. Generally, in the cationic electrodeposition coating process, the pH of water in the advanced rinsing process is about 6.0 to 7.0. The amount of paint to be brought out is 0.05-
About 0.2 mass% is contained, and pH has risen to about 6.5-7.0. If this is attempted to be filtered as it is by the ultrafiltration membrane (UF filtration device 9), the paint particles may coagulate and deposit on the ultrafiltration membrane. Therefore, as described above, in the closed system electrodeposition coating method of the present invention, in order to prevent this, it is preferable to keep the pH of the concentrated solution in the concentrating tank always at 6.4 or less.

As described above, by merely adjusting the pH of the concentrated water 21 to the above-mentioned predetermined range, the paint in the concentrated water 21 exists stably even under the pressure and shearing conditions in the UF filtration device 9, and the UF filtration device 9 It does not cause aggregation or clogging. The concentrated water 21 obtained by the membrane treatment as described above can be continuously circulated and concentrated through the UF filtration device, and can be concentrated up to a volume ratio of about 400 times. No trouble such as clogging occurs.

Further, in the electrodeposition coating apparatus of this embodiment, it is difficult to adjust the pH in the concentration tank 7 at the start of the operation, so that a certain amount of the overflow water is accumulated in the concentration tank 7 and the concentration tank 7 is concentrated. -Pipe d-UF filter 9-Pipe e-
It is preferable to adjust the pH of the liquid in the concentrating tank 7 to 6.0 or less at the initial stage of the operation until the circulation of the closed circuit Y including the concentrating tank 7 is started, and between 4.5 and 5.5. It is more preferable to adjust.

In order to adjust the pH of the liquid in these concentrating tanks, it is preferable to use at least one acid selected from the group consisting of organic acids, inorganic acids, and polar solutions. Organic acids that can be used include, for example, carboxylic acids, sulfonic acids, sulfuric acid esters, phosphoric acid esters, and phenols, and water-soluble carboxylic acids are preferable. As the water-soluble carboxylic acids, specifically, formic acid, acetic acid, propionic acid, butyric acid, lactic acid, citric acid, maleic acid, fumaric acid, oxalic acid, malic acid, tartaric acid, oxaloacetic acid,
Examples thereof include malonic acid, nitrilotriacetic acid, phthalic acid, trimellitic acid, and the like, with formic acid, acetic acid, and lactic acid being particularly preferable.

Examples of usable inorganic acids include sulfamic acid and carbonic acid. The above-mentioned polar liquid refers to a polar liquid discharged from the diaphragm device of the electrode in the electrodeposition tank 1, and contains the above-mentioned organic acid, inorganic acid and the like.

Although the closed system electrodeposition coating apparatus and the electrodeposition coating method of the present invention have been described above with reference to the preferred embodiments, the above embodiments are merely examples, and the present invention is not limited thereto. Instead, any conventionally known configuration can be diverted and / or added as long as the configuration of the present invention is provided. For example, in addition to the above configuration, other filtering means may be added to an appropriate place, or the principle of overflow may be used instead of the pump as a liquid feeding method. In addition, it is also possible to attach an appropriate pre-filter before each filtering means.

In the above description, the degree of enrichment means the rate of change with reference to the initial state of operation, and can be expressed as a volume ratio, a non-volatile matter concentration ratio, a conductive substance content ratio, etc. In this specification, it is expressed as a volume ratio. The volume ratio is defined as the ratio of the total volume of waste liquid sent to the concentrator to be treated to the volume of concentrate remaining in the concentrator.

[0041]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples. In this example and the comparative example, an experiment was carried out by appropriately modifying or changing the conditions of an electrodeposition coating apparatus in an actual automobile body coating line. Specifically, it is an electrodeposition coating apparatus having the configuration shown in FIG. 2, and the electrodeposition coating apparatus of the embodiment of the present invention is
The RO filtration device 10 and its associated pump 12, the pipes A, B, h, i, and the three-way valve 22 are removed, and all of the filtrate obtained by the UF filtration device 8 is sent to the recovery washing tank 4. To be In the following Examples and Comparative Examples, the non-volatile component in the concentrated liquid means 1
It means the residual component when it reaches a constant weight after drying at 10 ° C.

<Comparative Example 1> The automobile body coating line was operated for one day. The operating conditions at this time are as follows.

(Production conditions) -Number of products produced per day: 1000-Liquid level drop per day in the electrodeposition tank 1: 1.7
m ³ (Excluding the amount of replenishment paint. Normally, pure water is supplied in an amount that compensates for this drop in liquid level, but is not supplied in this example.)

(Conditions for electrodeposition coating) Electrodeposition coating 15: Cationic electrodeposition coating (Nippon Paint Co., Ltd.) controlled by NV (nonvolatile component concentration) = 20% by mass, pH = 6.3 and MEQ = 25. Made: Power Top (registered trademark) V-6), electrodeposition conditions: liquid temperature = 28 ° C, CV (painting voltage) = 30
0V, energizing time = about 3 minutes

(Conditions for advanced washing tank 6) -Amount of supplemental pure water D per day: 48 m ³ (= 50 liters / min.)-Conductivity of supplemental pure water D: 2.0 μS / cm (spray)

(Conditions of UF Filter 8) UF Membrane: KCV-301 manufactured by Asahi Kasei Corporation
0, processing capacity 2 liter / min. (Per module), 12 modules in total. Filtration conditions: input pressure = 2.5 kg / cm ² , output pressure = 0.
4 kg / cm ² · Amount of filtrate sent to the recovery water washing tank 4 = 34 m ³ , N of filtrate
V = 0.5 mass%

(Conditions of the UF filtration device 9) -Water quality of overflow water sent to the concentration tank 7: NV
= 0.1% by mass, pH = 6.2-pH of concentration tank 7: 6.0-UF membrane: Asahi Kasei Kogyo Co., Ltd., ECS-301
0, processing capacity 8 liters / min. (Per module), 25 modules in total. Filtration conditions: input pressure = 2.5 kg / cm ² , output pressure = 0.
5 kg / cm ² · Amount of filtrate sent to the advanced water washing tank 6 = 192 m ³ , amount of liquid drained from the cushion tank 25 outside the system = 48 m ³

-Concentration operation-When the line is not in operation, the concentrated water 21 (total amount of 15
m ³ ) is concentrated to 1.7 m ³ and the pump 13 is used for piping g
The solution was sent to the electrodeposition tank 15 through. At this time, the concentrated concentration NV of the concentrated concentrated water 21 was 10.5% by mass. Therefore, the paint solid content recovered in the advanced water washing system (closed circuit Y) was 179 kg as shown in the following formula. 1700 (liter) x 0.105 = 179 (kg)

Regarding the UF filter device 9 of the advanced water washing system,
The upper limit of concentration is designed to be about 5% by mass in NV, and the liquid permeation amount per module is 8 liters / min. Can be maintained. However, if the concentrated concentration is increased to about 10% by mass in NV and repeated, a high load is applied to the module and the amount of liquid permeation is reduced. In this example, the concentration N
By repeating the state of V = 10.6 mass% for 60 days, the liquid permeation amount per module was 6.5 liter / min. Fell to. Therefore, in this example, it is predicted that the module life will be shortened.

<Comparative Example 2> The concentration operation in Comparative Example 1 was changed so that the concentrated concentration NV of the concentrated water 21 in the concentrating tank 7 was 5% by mass when the line was not operating. 0.6 m ^{3 was} obtained. 1.7 of the obtained concentrated liquid
Regarding m ^3, it was decided to use the pump 13 to send the solution to the electrodeposition tank 15 through the pipe g, and discard the remaining 1.9 m ³ . Therefore, the paint solid content recovered in the advanced water washing system (closed circuit Y) is 85 kg as shown in the following formula,
g (179 kg-85 kg) have been discarded. 1700 (liter) x 0.05 = 85 (kg)

<Example 1> The electrodeposition coating apparatus used in the above comparative example was modified to obtain an electrodeposition coating apparatus having the configuration shown in FIG. Specifically, the RO filtration device 10, the pump 12 attached to the RO filtration device 10, and the pipes h and A are attached.
Since the experiment is performed using a real line, the three-way valve 22 and the pipes B and i are not installed in this embodiment,
The filtrate from the RO filtration device 10 was directly drained to the outside of the system. The comparative example 2 was operated in the same manner as the comparative example 2 except that the following conditions and the concentration operation were changed.

(Conditions of RO Filtration Device 10) RO Membrane: Nitto Denko Co., Ltd., NTR-7197 Filtration Conditions: Inlet pressure = 25 kg / cm ² , Outlet pressure = 24 k
g / cm ² , NV of the filtrate = 0.01% by mass ・ Amount of drainage of the filtrate from the pipe A per day: 1.9 m
³

In the same manner as in Comparative Example 2, 3.6 m ³ of concentrated liquid having a concentrated concentration NV of 5% by mass was obtained when the line was not in operation. In this example, all of the obtained concentrated liquid was sent to the electrodeposition tank 15 through the pipe g using the pump 13. Therefore, as in Comparative Example 1, 179 kg in the advanced water washing system (closed circuit Y)
Of paint solids were recovered.

Since the NV of the concentrated water 21 is adjusted to 5% by mass in the UF filtration device 9, the upper concentration limit NV = 5% by mass is maintained and the UF filtration device 9 is not loaded. The state of concentrated concentration NV = 5% by mass in this example was repeated for 60 days, but the amount of liquid per module did not decrease. Therefore, in this embodiment, it is predicted that the module life will not be shortened.

From the results of the above Examples and Comparative Examples, according to the present invention, the module in the UF filtration device 9 is not subjected to a high load, the life of the module is not shortened, and the paint components are discharged from the advanced rinsing step. Can be significantly reduced.

In this example, since the actual line was modified and experimented, various conditions could not be optimized, and the filtrate filtered by the RO filtration device 10 was used. Although it is simply discharged to the outside of the system, it is possible to efficiently use the water resources by adopting a configuration in which this is sent to the advanced water washing tank 5 or 6.

[0057]

As described above, according to the present invention,
With regard to the washing water in the advanced washing process, it is possible to reduce or eliminate the paint components to be discarded by reusing the paint components without causing an overload on the filtration device. It is possible to provide a closed system electrodeposition coating apparatus and an electrodeposition coating method that can achieve various closed types.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an outline of a closed system electrodeposition coating apparatus that is an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing an outline of an electrodeposition coating apparatus used in a comparative example.

[Explanation of symbols]

1 electrodeposition tank 2, 3, 4 recovery water washing tank 5, 6 Advanced washing tank 7 concentration tank 8, 9, 10 Filtration device 11, 12, 13, 14, 24 pumps 15 Electro-deposition paint 16, 17, 18 Recovery water wash water 19, 20 Rinse water 21 concentrated water 22 three-way valve 23 Filtrate tank 25 cushion tank A, B, a to i piping

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/44 C02F 1/44 F C25D 13/24 301 C25D 13/24 301A 301Z

Claims (2)

[Claims] 1. An electro-deposition tank containing at least an electro-deposition paint, in which an article to be coated is immersed and electro-deposition paint is applied, and the electro-deposition paint extracted from the electro-deposition tank is ultrafiltered, and the concentrated solution is subjected to First ultrafiltration means for returning to the electrodeposition tank, and recovered wash water containing the filtrate from the ultrafiltration means are stored, and the object to be electroplated in the electrodeposition tank is provided in each tank. A washing water containing one or two or more collecting water washing tanks, which is a pre-stage where the washing water is washed and the collected washing water is finally sent to the electrodeposition tank, and the washing water containing supplementary pure water is stored, 1 or 2 or more washing tanks for highly-washing the coated objects washed in one or two or more recovery washing tanks, and 2
In the case of more than the tank, the advanced washing tank in which the washing water is fed in the first stage, the concentration tank that receives the overflow water of the frontmost tank of the advanced washing tank, and the ultrafiltration of the water extracted from the concentration tank Then, the filtrate is sent to any of the advanced water washing tanks and / or removed outside the system, and the concentrated liquid is returned to the concentrated tank, whereby the water received in the concentrated tank is used as concentrated water. An electrodeposition coating apparatus comprising a second ultrafiltration means and a concentrated water delivery means for delivering the concentrated water to the electrodeposition tank, further comprising the first ultrafiltration means. A filtrate tank for storing the filtrate of the above, a recovered water washing water sending means for sending the liquid in the filtrate tank to the last stage of the recovered water washing tanks, and a liquid extracted from the filtrate tank is filtered by a reverse osmosis membrane. Reverse osmosis membrane filtration means for Return to the liquid tank, the filtrate of the reverse osmosis membrane filtration means,
A closed-system electrodeposition coating apparatus, characterized in that it is sent to any of the advanced water washing tanks and / or removed outside the system. 2. An electrodeposition coating step in which at least an object to be coated is immersed in an electrodeposition tank containing an electrodeposition paint, and one tank or two.
A recovery rinsing step of sequentially rinsing the object to be electro-deposited in the electrodeposition tank with the recovery rinsing water stored in the recovery rinsing tank of at least one tank and an advanced level of one or more tanks. An electrodeposition coating method comprising an advanced rinsing process in which each of the advanced rinsing tanks undergoes an advanced rinsing with the rinsing water containing supplementary pure water contained in the rinsing tank. In the case where the collected water in each of the collected water washing tanks in the collected water washing step is fed to the electrodeposition tank before the step, and the advanced water washing step has two or more advanced water washing tanks, The washing water of the advanced water washing tank is fed to the first stage, the overflow water of the first tank of the advanced water washing tank in the advanced water washing step is received in the concentration tank, and the water extracted from the concentration tank is ultrafiltered, The filtrate is stored in the advanced washing tank The water received in the concentrating tank is used as concentrated water by sending it to the crab and / or removing it outside the system and returning the concentrated solution to the concentrating tank. Liquid is sent to the electrodeposition tank, the electrodeposition coating material is extracted from the electrodeposition tank in the electrodeposition coating step, this is ultrafiltered, the concentrated solution is returned to the electrodeposition tank, and the filtrate is stored in the filtrate tank. , The liquid extracted from the filtrate tank is filtered by a reverse osmosis membrane, the concentrated liquid by the reverse osmosis membrane is returned to the filtrate tank, and the liquid in the filtrate tank is sent to the last tank of the recovery washing tank. On the other hand, the closed system electrodeposition coating method, characterized in that the filtrate is sent to one of the advanced water washing tanks and / or removed outside the system.